While the alkylation of aromatic compounds with catalysts, such as the zeolites, is not novel, the alkylation of phosphate aromatic esters, as exemplified by triphenylphosphate is quite distinguishable and poses some unique problems. Even though triphenylphosphate possesses aromatic rings, the high polarity of the phosphate moiety distinguishes this compound from non-polar aromatic compounds. Most importantly, cracking of triphenylphosphate is a serious problem in the presence of an acidic catalyst, whereas such a problem does not exist for aromatic compounds. As a result, the alkylation of phosphate aromatic esters becomes considerably more difficult and requires different catalysts and process conditions as compared to those needed for the alkylation of non-polar aromatic compounds. Many catalysts that work for aromatic alkylation fail to work for triphenylphosphate alkylation.
British Patent No. 1,369,346 describes the alkylation of triphenylphosphate at elevated temperature and pressure employing a catalyst that is an aryloxide of aluminum, zirconium, hafnium, niobium, or tantalum, an aryl sulfonic acid, sulfuric acid, an alumina clay, or an acid-activated silica-alumina clay.